Understanding Deep Vein Thrombosis

Deep vein thrombosis (DVT) is a condition in which a blood clot, or thrombus, forms in a deep vein. A blood clot is most common in the leg. But it can form in a large vein deep inside the leg, arm, or other part of the body. DVTs are dangerous because part of the clot, called an embolus, can separate from the vein. It may travel to the lungs and form a pulmonary embolus (PE). This can cut off blood flow to part of the lung or to the entire lung. A PE is a medical emergency and may cause death. Doctors use the term venous thromboembolism (VTE) to describe the two conditions, DVT and PE. They use the term VTE because the two conditions are very closely related. Their prevention and treatment also are closely related.

Over time, a blood clot can also permanently damage veins. To protect your health, a blood clot must be treated right away.

How DVT develops

The deep veins of the legs are located in the muscles. These veins help carry blood from the legs up to the heart. When leg muscles contract and relax, blood is squeezed through the veins back to the heart. One-way valves inside the veins help keep the blood moving in the right direction. When blood moves too slowly or not at all, it can pool in the veins. This makes a clot more likely to form.

Cross section of muscle and vein showing open valve with arrow showing blood moving up. Cross section of varicose vein with thrombus and emboli.

Risk factors

Anyone can get a blood clot. Risk factors that make a blood clot more likely to happen include:

  • Being inactive for a long time, such as when you’re in the hospital or traveling by plane or car.

  • An injured vein due to an accident, a broken bone, or surgery.

  • A history of blood clots. 

  • A personal or family history of a blood-clotting disorder.

  • Recent surgery.

  • Cancer and certain cancer treatments.

  • Smoking.

Other things can also put you at higher risk for a blood clot. They include:

  • Being older than 60.

  • Pregnancy.

  • Taking birth control or hormone replacement.

  • Having other vein problems.

  • Being a higher-weight person.

  • Having diabetes.

Common symptoms

A blood clot doesn't always cause obvious symptoms. If you do have symptoms, they often happen suddenly. They may include:

  • Pain, especially deep in the muscle.

  • Swelling.

  • Aching or soreness.

  • Red or warm skin.

  • A fever.

When to call your doctor

Contact your doctor right away if you have any of the common symptoms listed above.

And contact your doctor if you have symptoms of bleeding such as:

  • Blood in the urine.

  • Bleeding with bowel movements.

  • Bleeding from the nose, gums, a cut, or the vagina.

Call 911

Call 911 if you have symptoms of pulmonary embolism such as:

  • Trouble breathing.

  • A fast heartbeat.

  • Chest pain.

  • Sweating.

  • Coughing (may cough up blood).

  • Fainting.

If you take medicine to help prevent blood clots, you have an increased risk of bleeding. Also call 911 if you have heavy or uncontrolled bleeding.

Diagnosing DVT

Your doctor will start with questions about your symptoms and health history along with a physical exam.

Diagnostic tests include:

  • An imaging test called a duplex ultrasound. This test uses sound waves to create pictures of veins and blood flow.

  • Blood tests. These are done to check for clotting and other problems.

If your doctor thinks you may have pulmonary embolism, more testing will be done.

Treating DVT

Treating a blood clot may include:

  • Medicine to thin the blood and prevent pulmonary embolism and other complications.

  • A stay in the hospital. This may or may not be needed.

  • Surgery, in some cases.

Preventing DVT

Many people who are in the hospital are at higher risk of developing blood clots. So preventing blood clots is an important part of in-hospital care. The care may include getting out of bed regularly, taking medicine, or using special therapies or devices. Other factors and conditions may increase the risk of blood clots. Review your risk with your doctor.